656 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



nerve, or they may only become so in anaesthetised animals after some 

 delay. 



In the frog the development of the paralytic symptoms in the eye 

 (and tongue), after section of the sympathetic or extirpation of the 

 superior-cervical ganglion, is usually, if not always, gradual. 



In the rabbit there is an early stage in the condition of the pupil, 1 

 after section of the post-ganglionic fibres, which has not been noticed in 

 the cat or dog. After about twenty-four hours the pupil begins to 

 dilate, slowly enlarges, and on the third to the fifth day again becomes 

 small and remains smaller than normal. This may be taken to be due 

 to stimuli set up in the fibres during degeneration, though it is curious 

 that this reaction of degeneration should not occur, so far as we know, 

 in the vaso-constrictor fibres of the rabbit, or in any of the fibres in the 

 sympathetic of the cat and dog. 



Apart from this temporary escape from the effect of section, there is, 

 in all animals, as time goes on, some degree of return to the normal 

 condition. This varies in different animals ; there is much difference of 

 opinion with regard to it. The recovery is generally held to be greater 

 and more complete in the rabbit than in the cat and dog. 



Section of the cervical sympathetic causes a permanent diminution 

 in the size of the pupil. In the cat and dog this is obvious, in the 

 rabbit it is much less ; even a week or two only after section, the 

 difference from the normal pupil may be very slight. 



Less attention has been paid to the other effects produced on the eye 

 by section of the nerve. In the cat, the narrowing in the palpebral 

 fissure is for several months more or less obvious on the side of the 

 lesion ; the nictitating membrane, which for a few days covers 

 about a half of the cornea, is gradually withdrawn until it projects 

 very little more than the normal one. The increase in the secretion 

 poured on the surface of the eye lasts in the dog two or three 

 weeks only. 



The nictitating membrane does not maintain a constant position ; a month 

 or more after section, it may at times be almost completely withdrawn, and at 

 times project and cover about a third of the cornea. 



As we have said, the great dilatation of the vessels of the ear, which is 

 seen in the first few days after section of the cervical sympathetic, or 

 after excision of the superior cervical ganglion, gradually diminishes, at 

 any rate as a rule. 



Not infrequently in the rabbit the vessels of the ear on the 

 side of the lesion return nearly to normal in four or five days. 

 The rapid recovery in these cases we must attribute to the pre- 

 sence of uncut vasomotor fibres, passing to the ear by way of the 

 vertebral ramus of the ganglion stellatum and the great auricular 

 nerve (cf. p. 624). 



In the cat and dog the decrease in the flushing is slow, going on for 

 some weeks ; and it is doubtful whether the normal tone is ever 

 completely regained. In some cases, indeed, in the rabbit as well as in 

 the cat and dog, it is said that the paralytic effects continue for 

 a very long period — a year and more — without any considerable 

 diminution. 



1 This was first noticed by Budge, "Ueberd. Bewegung. d. Iris," Braunschweig, 1855, 

 S. 125. 





